1. Field of the Invention
The present invention relates to an electromagnetic brake and a drive force distributing apparatus for a vehicle using the electromagnetic brake.
2. Description of the Related Art
A differential is located in a power train of a vehicle to maintain torque distribution between right and left wheels of the vehicle such that torque is equally divided between the right and left wheels and to rotate the outside wheel faster than the inside wheel during cornering, thereby reliably obtain smooth cornering. While the primary role of the differential is to obtain smooth cornering as mentioned above, there is a case that one of the right and left wheels may be caught to slip in a muddy place during rough-road running.
In this case, the resistance from the road to the wheel caught to slip in the muddy place is small, so that torque is almost transmitted to this slipping wheel and hardly transmitted to the other wheel. As a result, there is a problem that the slipping wheel cannot escape from the muddy place for lack of the drive force for driving the wheels. This is a problem in a defect inherent in a general differential. Known is a special type of differential having a differential motion limiting mechanism capable of compensating for the above defect inherent in a general differential. This type of differential is referred to as a limited slip differential (LSD).
A planetary gear type differential is generally known in the art, for example, such a planetary gear type differential gear assembly having a limited slip differential mechanism composed of an electromagnetic clutch and a multiplate clutch is disclosed in Japanese Patent Laid-open No. Hei 6-33997. In this differential gear assembly, an attraction force between a solenoid and an armature forming the electromagnetic clutch is applied to the multiplate clutch to press it and selectively control an engaging force generated in the multiplate clutch. A connecting member consisting of a plurality of bars is located between a pressure plate of the multiplate clutch and the armature. That is, one end of each bar of the connecting member is fixed to the pressure plate of the multiplate clutch, and the other end abuts against an inner circumferential portion of the armature when the solenoid is operated.
In the conventional differential gear assembly mentioned above, the plural bars fixed to the pressure plate extend in a direction substantially perpendicular to the pressure plate. Accordingly, in the case that any of these bars are inclined to the pressure plate, there is a problem that a pressing force of the armature attracted by the solenoid to press the pressure plate of the multiplate clutch may not be uniformly transmitted to the pressure plate. Further, in the conventional differential gear assembly described in the above publication, the electromagnetic clutch controls the engaging force of the multiplate clutch, so that the plural bars as pressure members are located so as to correspond to the inner circumferential portion of the armature. However, in a multiplate brake structure having a plurality of brake plates and a plurality of brake discs, these brake plates and brake discs are generally located so as to correspond to an outer circumferential portion of the armature from the viewpoint of the structure. Accordingly, it is difficult that the conventional structure described in the above publication such that the multiplate clutch is operatively connected to the armature at its inner circumferential portion is applied to the multiplate brake structure without any changes.